Propshafts are commonly employed for transmitting power from a rotational power source, such as the output shaft of a vehicle transmission, to a rotatably driven mechanism, such as a differential assembly. As is well known in the art, propshafts tend to transmit vibration while transferring rotary power. When the propshaft is excited at a harmonic frequency, vibration and noise may be amplified, creating disturbances that are undesirable to passengers riding in the vehicle. Thus, it is desirable and advantageous to attenuate vibrations within the propshaft in order to reduce noise within the vehicle passenger compartment.
Various devices have been employed to attenuate the propagation of noise from propshafts including inserts that are made from cardboard, foam, or resilient materials, such as rubber. The inserts that are typically used for a given propshaft are generally of a construction, size, mass and density to attenuate bending mode vibrations within the propshaft. While such inserts offer various advantages, several drawbacks remain.
One such drawback is the susceptibility of current propshaft assemblies to experience shell mode vibrations in the environment in which they are installed. Long aluminum propshafts have been found to produce significant noise resulting from the propshaft being excited at a shell mode natural frequency. Previously known inserts operable to attenuate propshaft tube vibrations are typically heavy and inefficient in attenuating both bending and shell mode vibrations. For long aluminum propshafts that are generally obliged to have damping treatments, these known inserts many times create concerns regarding to their mass loading effect on critical speed as well as their effectiveness on tube shell mode vibrations. It is therefore desirable to provide an improved propshaft with a lightweight however highly efficient damping treatment that is operable to attenuate propshaft tube vibrations to reduce noise transmitted to the vehicle occupants.
Furthermore, because different propshaft structures may exhibit different shell mode natural frequencies, it may be desirable to provide a propshaft assembly having an insert operable to be tuned to attenuate specific shell mode natural frequencies.